$3$ Combined Section with Combined Loading

Consider the beam cross$-$section below. It is constructed of aluminum, with $G=25$GPa and $E=70$GPa. Each portion is $3$ mm thick, except for web $36,$ which has thickness $t_{36}=4mm.$ A shear load of $70$ kN is applied along the web $567,$ as indicated below. Compute the rate of twist $d\frac{}{d}z.$ Identify the maximum and minimum shear stresses, and the locations at which they occur.